Question

When a resistance connected in series with a cell is halved, the current is not exactly doubled but slightly less. Why???

Answer 1

because voltage given by a cell is V = e -ir where r is internal resistance and e is electromotive force and i is current.
e = iR where R is external resistance
so
v = iR - ir
when you half R, you will get a little less than double current because i = v/(R - r) NOT v/R.
this is only because of internal resistance of battery

Answer 2

Answer:

This is owing to the internal resistance r of the cell. The current delivered by the cell is

I=E/R+r

When external resistance R is made R/2, the current will be slightly less than 2I.

Explanation: